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Kustom K200b1 schematic [message #29736]

Thu, 25 June 2026 13:40

bshawkes
Messages: 9
Registered: April 2026

Junior Member

Hi Everyone, I'm looking for a Kustom K200b1 schematic. I've seen others looking for the same one but I can't seem to find the technical information section. Can anyone direct me to the schematic or the section where it is located??

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Re: Kustom K200b1 schematic [message #29737 is a reply to message #29736]

Thu, 25 June 2026 18:20

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

Hello.
When you first get on this sites home page on the left hand side one of the listings is Technical.

Click on that and you will see that you can view amp schematics by the whole amp or just by PC board you want to look at.

What is the issue with your amp?

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Re: Kustom K200b1 schematic [message #29738 is a reply to message #29737]

Thu, 25 June 2026 18:25

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

Note that until you have made 5 post that I approve first your post will not automatically go up to the web board.
Sorry for the inconvenience but this does away with all spam.

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Re: Kustom K200b1 schematic [message #29739 is a reply to message #29738]

Thu, 25 June 2026 18:37

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

Hello again.
I need to correct my first reply to you.

Under the amp listing when you open it you only get the main layout and the power supply schematic.
For the schematics of the 3 circuit boards in that amp you need to go to the other part of the technical section that shows the PC board listings.

So you want PC 105, PC 203 and PC 703.

Note that there are revisions to some of these boards and the markings on your board will reference that , like for example PC703 rev 1.

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Re: Kustom K200b1 schematic [message #29740 is a reply to message #29737]

Fri, 26 June 2026 11:33

bshawkes
Messages: 9
Registered: April 2026

Junior Member

stevem wrote on Thu, 25 June 2026 18:20

Hello.
When you first get on this sites home page on the left hand side one of the listings is Technical.

Click on that and you will see that you can view amp schematics by the whole amp or just by PC board you want to look at.

What is the issue with your amp?

As soon as I turn on the amp it starts making a crackling noise and within a minute the output cuts out. It does the weather there is a cable plugged into any input or no cable at all.

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Re: Kustom K200b1 schematic [message #29741 is a reply to message #29739]

Fri, 26 June 2026 11:39

bshawkes
Messages: 9
Registered: April 2026

Junior Member

stevem wrote on Thu, 25 June 2026 18:37

Hello again.
I need to correct my first reply to you.

Under the amp listing when you open it you only get the main layout and the power supply schematic.
For the schematics of the 3 circuit boards in that amp you need to go to the other part of the technical section that shows the PC board listings.

So you want PC 105, PC 203 and PC 703.

Note that there are revisions to some of these boards and the markings on your board will reference that , like for example PC703 rev 1.

Thanks I found the correct page for technical info, but when I try to select any of the 3 PCB's for the K200b1 that links say that the doc's are not available.

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Re: Kustom K200b1 schematic [message #29742 is a reply to message #29741]

Fri, 26 June 2026 13:16

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

Boy, this problem is one that needs to narrowed down section by section.

In your amp the the audio output wires from each preamp board mounted on the front of the amp are blue in color and those two wires go into the left side of the 703 board on the rear wall of the amp.

I would clip each of those blue wires one at a time to see if the noise you have stops as that would narrow the issue down to either the 105 or 203 preamp board.

If not then the issue is on the 703 board or the other components mounted on the chassis .

To find the schematics you need when you get to the technical section choose the second listing which says “schematics by PC number “. Then you can pick the PC number you want to look at.

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Re: Kustom K200b1 schematic [message #29743 is a reply to message #29742]

Fri, 26 June 2026 13:20

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

Just clip those wires and you can put them back together with crimp type butt connectors and then you will not have to remove the 703 board from the rear wall to unsolder them.

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Re: Kustom K200b1 schematic [message #29744 is a reply to message #29742]

Fri, 26 June 2026 13:35

bshawkes
Messages: 9
Registered: April 2026

Junior Member

I'll try your suggestions Thanks !!

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Re: Kustom K200b1 schematic [message #29745 is a reply to message #29736]

Sun, 28 June 2026 12:24

bshawkes
Messages: 9
Registered: April 2026

Junior Member

UPDATE!! I have checked the green and red wires for the +8 and -8 dc voltage and they were both there. When I cut the blue wires from the pre-amp boards I still have the crackling noise. Another thing that happened was just before I went to measure the +8/-8 voltage the crackling stopped and when i measured the voltage there was no voltage, then the crackling noise started again and the voltage was there. Any help would be great !!

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Re: Kustom K200b1 schematic [message #29746 is a reply to message #29745]

Sun, 28 June 2026 14:09

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

Well in a way that’s good news because there’s only a few things that would make both 8 volts supplies cut out.

When I get home this evening I will post you up a reply on that.

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Re: Kustom K200b1 schematic [message #29747 is a reply to message #29746]

Sun, 28 June 2026 17:03

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

To narrow this problem more I need to know if the pilot lamp goes out when both 8 volt supplies go down?

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Re: Kustom K200b1 schematic [message #29748 is a reply to message #29747]

Sun, 28 June 2026 20:03

bshawkes
Messages: 9
Registered: April 2026

Junior Member

the lamp stayed on as far as I remember

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Re: Kustom K200b1 schematic [message #29749 is a reply to message #29748]

Mon, 29 June 2026 04:52

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

If indeed the lamp is staying on then I would have to say that you have a bad connection on the screw down wires on the top of the two main filter cans, and especially the black center grounding wire.

If not that then it must be the + 40 and -40 volt input connection from those can filters to the 703 board where that 40 volts is regulated down to 8.

If the lamp does go out then there’s other failure possibility’s.

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Re: Kustom K200b1 schematic [message #29750 is a reply to message #29749]

Mon, 29 June 2026 10:28

bshawkes
Messages: 9
Registered: April 2026

Junior Member

stevem wrote on Mon, 29 June 2026 04:52

If indeed the lamp is staying on then I would have to say that you have a bad connection on the screw down wires on the top of the two main filter cans, and especially the black center grounding wire.

If not that then it must be the + 40 and -40 volt input connection from those can filters to the 703 board where that 40 volts is regulated down to 8.

If the lamp does go out then there’s other failure possibility’s.

Thanks. I was thinking of replacing the filter caps just from age. I'll also look for cold solder joint on the 703 board and I'll keep an eye on the lamp to confirm its status.

another thing I forgot to mention was I put a 1k signal for a signal generator thru and notice that there was a large drop of the signal from the input jack to where in connects to the 703 board (I used a oscilloscope to trace it).

I'll let you know what happens.

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Re: Kustom K200b1 schematic [message #29751 is a reply to message #29750]

Tue, 30 June 2026 05:59

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

I would not replace the two main rail filters just yet since,

1) there not likely to be the cause of your issue.

2) there like 60 bucks each if not more.

It’s takes a large amount of preamp output signal to drive the 703 board, I forget exactly how much that is, but I am certain it’s over 3 volts.

Can your signal generator out put that much?

In terms of input signal level at the front of the amp it only takes 150 MV to drive a fully good amp to peak wattage into a 4 ohm load.

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Re: Kustom K200b1 schematic [message #29753 is a reply to message #29751]

Thu, 02 July 2026 11:22

bshawkes
Messages: 9
Registered: April 2026

Junior Member

AI says this is what my signal generator puts out "The Hickok Model 5900A (a vintage test instrument) puts out a maximum waveform amplitude of 20 volts peak-to-peak (into a high-impedance load) or 10 volts peak-to-peak into a standard 50-ohm load.

If I use the signal generator or a guitar the output is almost nothing and is very fuzzy. and that is even if I can get any output.

I was thing of recapping the 703 board just as a place to start and due to the age of the caps.

Any thoughts??

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Re: Kustom K200b1 schematic [message #29754 is a reply to message #29753]

Fri, 03 July 2026 08:55

stevem
Messages: 4904
Registered: June 2004
Location: NY

Senior Member

Hi.

If you have 39.5 volts positive and negative coming out of the big main rail can filters with less then 1 volt of ac out of them feeding into the 703 then there not an issue.

Note that with the way the 8 volt plus and minus regulators are set up that the negative regulator tracks the positive one.
If the positive one is not right then the negative one will be off also.

Before replacing all the caps on the 703 board I would disconnect the green and red wires from each preamp board one at a time to see if a bad preamp board is loading down the low voltage supplies.

You must disconnect both the red and green power supply wires feeding each preamp board, as having just one working supply will harm the preamp board.

If you find a bad preamp board then try putting a 2 volt test tone into the 703 board to see if that works ok on its own.

If nothing comes from that then try recapping the 703 board.

Note that the bias diode clipped in between the output transistors has very fragile leads so be really careful with it.

If one of those leads break and you power on the amp that will blow the whole output section .

What I do is put good size dab of silicone tub calk on the diode and each lead on the board so they can not be bent at a sharp angle which will cause them to snap.

[Updated on: Fri, 03 July 2026 08:57]

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Re: Kustom K200b1 schematic [message #29755 is a reply to message #29754]

Mon, 06 July 2026 10:13

bshawkes
Messages: 9
Registered: April 2026

Junior Member

Thanks for the info. I'll let you know what I find.

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